Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $102.85   10.197%   $113.3376   $113.34   $113.35   $113.30  
  Purchase #2 $246.95   11.221%   $274.6603   $274.66   $274.65   $274.70  
  Purchase #3 $139.48   9.807%   $153.1588   $153.16   $153.15   $153.20  
  Purchase #4 $163.50   5.177%   $171.9644   $171.96   $171.95   $172.00  
  Purchase #5 $76.35   11.438%   $85.0829   $85.08   $85.10   $85.10  
  Purchase #6 $127.36   12.442%   $143.2061   $143.21   $143.20   $143.20  
  Purchase #7 $139.60   11.230%   $155.2771   $155.28   $155.30   $155.30  
  7 purchase totals = $996.09       $1,096.6872   $1,096.69   $1,096.70   $1,096.80