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 $60.70   7.132%   $65.0291   $65.03   $65.05   $65.00  
  Purchase #2 $75.71   8.268%   $81.9697   $81.97   $81.95   $82.00  
  Purchase #3 $130.95   8.173%   $141.6525   $141.65   $141.65   $141.70  
  Purchase #4 $91.36   10.534%   $100.9839   $100.98   $101.00   $101.00  
  Purchase #5 $135.79   10.355%   $149.8511   $149.85   $149.85   $149.90  
  Purchase #6 $138.65   10.373%   $153.0322   $153.03   $153.05   $153.00  
  Purchase #7 $201.50   10.699%   $223.0585   $223.06   $223.05   $223.10  
  7 purchase totals = $834.66       $915.5770   $915.57   $915.60   $915.70