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 $94.35   11.368%   $105.0757   $105.08   $105.10   $105.10  
  Purchase #2 $209.39   6.755%   $223.5343   $223.53   $223.55   $223.50  
  Purchase #3 $119.31   8.794%   $129.8021   $129.80   $129.80   $129.80  
  Purchase #4 $50.34   12.566%   $56.6657   $56.67   $56.65   $56.70  
  Purchase #5 $184.79   8.572%   $200.6302   $200.63   $200.65   $200.60  
  Purchase #6 $159.73   13.639%   $181.5156   $181.52   $181.50   $181.50  
  Purchase #7 $96.80   6.490%   $103.0823   $103.08   $103.10   $103.10  
  7 purchase totals = $914.71       $1,000.3059   $1,000.31   $1,000.35   $1,000.30