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 $75.74   12.374%   $85.1121   $85.11   $85.10   $85.10  
  Purchase #2 $134.34   11.171%   $149.3471   $149.35   $149.35   $149.30  
  Purchase #3 $23.72   7.850%   $25.582   $25.58   $25.60   $25.60  
  Purchase #4 $133.62   10.203%   $147.2532   $147.25   $147.25   $147.30  
  Purchase #5 $55.43   6.223%   $58.8794   $58.88   $58.90   $58.90  
  Purchase #6 $67.52   11.537%   $75.3098   $75.31   $75.30   $75.30  
  Purchase #7 $206.29   9.354%   $225.5864   $225.59   $225.60   $225.60  
  7 purchase totals = $696.66       $767.0700   $767.07   $767.10   $767.10