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 $213.82   8.812%   $232.6618   $232.66   $232.65   $232.70  
  Purchase #2 $193.86   9.367%   $212.0189   $212.02   $212.00   $212.00  
  Purchase #3 $37.90   7.213%   $40.6337   $40.63   $40.65   $40.60  
  Purchase #4 $201.53   12.813%   $227.352   $227.35   $227.35   $227.40  
  Purchase #5 $67.57   9.776%   $74.1756   $74.18   $74.20   $74.20  
  Purchase #6 $135.75   9.495%   $148.6395   $148.64   $148.65   $148.60  
  Purchase #7 $145.45   11.317%   $161.9106   $161.91   $161.90   $161.90  
  7 purchase totals = $995.88       $1,097.3921   $1,097.39   $1,097.40   $1,097.40