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 $172.98   7.527%   $186.0002   $186.00   $186.00   $186.00  
  Purchase #2 $111.27   9.311%   $121.6303   $121.63   $121.65   $121.60  
  Purchase #3 $181.41   7.132%   $194.3482   $194.35   $194.35   $194.30  
  Purchase #4 $248.31   6.185%   $263.668   $263.67   $263.65   $263.70  
  Purchase #5 $18.30   8.662%   $19.8851   $19.89   $19.90   $19.90  
  Purchase #6 $62.78   10.869%   $69.6036   $69.60   $69.60   $69.60  
  Purchase #7 $185.33   9.516%   $202.966   $202.97   $202.95   $203.00  
  7 purchase totals = $980.38       $1,058.1014   $1,058.11   $1,058.10   $1,058.10