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 $88.50   6.433%   $94.1932   $94.19   $94.20   $94.20  
  Purchase #2 $189.94   3.568%   $196.7171   $196.72   $196.70   $196.70  
  Purchase #3 $243.98   3.253%   $251.9167   $251.92   $251.90   $251.90  
  Purchase #4 $176.30   3.138%   $181.8323   $181.83   $181.85   $181.80  
  Purchase #5 $218.70   9.210%   $238.8423   $238.84   $238.85   $238.80  
  Purchase #6 $217.98   13.583%   $247.5882   $247.59   $247.60   $247.60  
  Purchase #7 $198.59   6.290%   $211.0813   $211.08   $211.10   $211.10  
  7 purchase totals = $1,333.99       $1,422.1711   $1,422.17   $1,422.20   $1,422.10