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 $74.78   12.369%   $84.0295   $84.03   $84.05   $84.00  
  Purchase #2 $184.66   3.679%   $191.4536   $191.45   $191.45   $191.50  
  Purchase #3 $52.35   10.341%   $57.7635   $57.76   $57.75   $57.80  
  Purchase #4 $235.97   3.247%   $243.6319   $243.63   $243.65   $243.60  
  Purchase #5 $121.33   9.146%   $132.4268   $132.43   $132.45   $132.40  
  Purchase #6 $55.35   10.385%   $61.0981   $61.10   $61.10   $61.10  
  Purchase #7 $226.43   7.668%   $243.7927   $243.79   $243.80   $243.80  
  7 purchase totals = $950.87       $1,014.1961   $1,014.19   $1,014.25   $1,014.20