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 $160.53   10.654%   $177.6329   $177.63   $177.65   $177.60  
  Purchase #2 $90.96   4.171%   $94.7539   $94.75   $94.75   $94.80  
  Purchase #3 $121.45   10.606%   $134.331   $134.33   $134.35   $134.30  
  Purchase #4 $151.89   10.344%   $167.6015   $167.60   $167.60   $167.60  
  Purchase #5 $76.92   4.572%   $80.4368   $80.44   $80.45   $80.40  
  Purchase #6 $166.27   3.543%   $172.1609   $172.16   $172.15   $172.20  
  Purchase #7 $110.45   7.478%   $118.7095   $118.71   $118.70   $118.70  
  7 purchase totals = $878.47       $945.6265   $945.62   $945.65   $945.60