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 $197.71   6.240%   $210.0471   $210.05   $210.05   $210.00  
  Purchase #2 $187.29   8.546%   $203.2958   $203.30   $203.30   $203.30  
  Purchase #3 $69.43   7.459%   $74.6088   $74.61   $74.60   $74.60  
  Purchase #4 $132.42   9.503%   $145.0039   $145.00   $145.00   $145.00  
  Purchase #5 $207.55   9.282%   $226.8148   $226.81   $226.80   $226.80  
  Purchase #6 $57.92   9.668%   $63.5197   $63.52   $63.50   $63.50  
  Purchase #7 $88.95   12.169%   $99.7743   $99.77   $99.75   $99.80  
  7 purchase totals = $941.27       $1,023.0644   $1,023.06   $1,023.00   $1,023.00